This invention relates to a process for the improvement of the color and color stability of a hydrocarbon fraction. In one aspect, this invention relates to a catalytic selective hydrogenation treatment of a hydrocarbon fraction to render the hydrocarbon fraction color stable.
The improvement of color stability of a hydrocarbon fraction (and kerosene in particular) is desirable because it increases the marketability of the hydrocarbon fraction. For example, kerosene used as a carrier for insecticides and similar materials should be substantially colorless and color-stable in order to avoid staining materials with which it may come in contact. When kerosene or other hydrocarbon fractions are used as jet fuel, thinners or vehicles for paints or coatings, color stability is also very desirable.
There are several methods known in the art to improve both the color and color stability of hydrocarbon fractions in general and kerosene in particular. For example, a hydrocarbon fraction may be processed through an adsorbent (usually a clay) to remove the color bodies. However, because clays are very expensive, this type of treating process is rarely used. Another method is hydrogenation as shown in U.S. Pat. No. 2,793,986 which discloses treating kerosene at a temperature of 500.degree. to 650.degree. F. at a pressure of 100 to 250 p.s.i. and a hydrogen flow of 1,000 to 5,000 cubic feet per barrel of kerosene treated. The treatment is conducted in the presence of a molybdenum oxide/silica/alumina catalyst. These conditions are extremely severe and not only hydrogenate the color bodies, but would also hydrogenate olefins, aromatics and nitrogen and sulfur compounds (to ammonia and hydrogen sulfide respectively). This is usually referred to as hydrotreating.
The disadvantages to hydrotreating are that it costs about 50 cents to one dollar per barrel to run, it alters the major components of the fraction, and it consumes large quantities of hydrogen. Therefore, there is a need for a process which would render a hydrocarbon fraction color stable but does not cost as much to operate, consume large quantities of hydrogen, or alter the major components of the hydrocarbon fraction.
Applicants have discovered a process that fills this need. Applicants' process is a selective hydrogenation process. Thus, applicants' process uses only about 0.1 to 2 cubic feet of hydrogen per barrel of kerosene versus 1,000 to 5,000 cubic feet per barrel required by the '986 patent. According to the '986 patent, pressures below 100 p.s.i. result in improved color only in the case of untreated kerosenes already having extremely high color. Applicants have found that any type of kerosene can be treated at pressures below 100 psi. The instant invention can be run at a temperature as low as 25.degree. C. whereas the lowest temperature at which the '986 process can be run is 260.degree. C.
Applicants' process also does not alter the major components of the hydrocarbon fraction. This is evidenced by the fact that the amount of aromatics present in the hydrocarbon fraction is substantially the same before and after treating. Thus, only the color bodies and color body precursors are being hydrogenated. The instant process represents a significant advance in the art of rendering hydrocarbon fractions color stable.